a) Field of the Invention
This invention relates to a damper structure suitable for use in a power transmission mechanism of a vehicle.
b) Description of the Related Art
With reference to FIG. 7 through FIG. 11, a description will first be made of a conventional damper structure as used by way of example in a lockup clutch for a torque converter. FIG. 7 is a front view of a spring assembly 51, and FIG. 8 is a cross-sectional view taken along the line VIIIxe2x80x94VIII of FIG. 7. Springs 53 are carried on their corresponding retainer plates 57. The retainer plates 57 are fixed on a core plate 52 by rivets 55 such that the retainer plates 57 are arranged with equal intervals. On opposite end portions of each spring 53, caps 58 are fitted such that the spring 53 can be pressed in a well-balanced state.
Each retainer plate 57 is composed of an upper plate 61 and a lower plate 62. The upper plate 61 is provided with a tab 61A and bent portions 61B. The tab 61 has been formed by slitting a part of the upper plate 61 and bending up the slit part, and holds the corresponding spring 53 at its inner periphery. The bent portions 61B extend along opposite ends of the spring 53, respectively, and support the spring 53 at its opposite ends. A bent portion 62A is arranged on and along an outer periphery of the lower plate 62, and supports and holds the spring 53 at its outer periphery.
FIG. 9 is a front view of a conventional driven plate 70 in the conventional damper structure, and FIG. 10 is a cross-sectional view of the conventional driven plate 70 taken in an axial direction of FIG. 9. The driven plate 70 includes a ring-shaped core plate 72 and flanges 71 formed by bending up outer peripheral edge portions of the core plate 72. Adjacent opposite ends of each flange 71, the core plate 72 includes relieves 73 arranged to facilitate bending operation upon formation of the driven plate 70.
FIG. 11 illustrates the conventional damper structure 60 constructed in combination of the above-mentioned spring assembly 51 and the driven plate 70. As a result of pressing by the flanges 71 of the driven plate 70, said flanges 71 being counterpart members on the spring assembly 51, and the corresponding springs 53 against each other via the associated caps 58, power is transmitted between the side of the spring assembly 51 and the side of the driven plate 70. Vibrations, which occur at the time of the power transmission, are absorbed by the springs 53.
Numeral 59 indicates a friction member, which is required when the core plate 52 is arranged as a lockup piston.
In the conventional damper structure described above, the driven plate 70 is rotatable over a range of the angular interval between the adjacent springs 53 arranged in the spring assembly 51. Accordingly, the range of relative rotation between the driven plate 70 and the spring assembly 51 is large. Especially when the damper structure is used as a damper in a lockup clutch for a torque converter, large loads are applied to the springs because the damper is affected considerably by torque fluctuations of an engine as a power source. Accordingly, there has been a high potential risk that the springs may be permanently set in fatigue or may be broken.
An object of the present invention is, therefore, to provide a damper structure, which can limit an input of an excessive load onto each spring and can protect the spring from permanent setting in fatigue or breakage. Another object of the present invention is to provide a lockup clutch provided with the damper structure and suitable for use in a torque converter.
In one aspect of the present invention, there is thus provided a damper structure constructed of a core plate, a retainer plate fixed on the core plate, a spring assembly carried on the retainer plate and having at least one spring, and a driven plate arranged coaxially with the spring assembly and having a flange engageable with the spring, wherein the retainer plate is composed of an upper plate and a lower plate, the upper plate is provided with a lug portion formed by slitting a part of the upper plate and bending the slit part, the driven plate is provided with a stopper engageable with the lug portion. The stopper may preferably be arranged such that the stopper is brought into contact with the lug portion shortly before the spring would be fully compressed as a result of pressing by the spring and the flange against each other. Preferably, the spring assembly have a plurality of springs and the driven plate have a like plural number of flanges.
In another aspect of the present invention, there is also provided a lockup clutch suitable for use in a torque converter, wherein the lockup clutch comprises the above-described damper structure.
Owing to the above-described construction, the damper structure according to the present invention can bring about an advantageous effect that the spring or springs can be protected from permanent setting in fatigue or breakage.